This invention relates to lithography apparatus and methods of performing lithographic exposure, commonly used to transfer a pattern onto a substrate in order to manufacture devices such as, for example, semiconductor devices, liquid crystal displays, etc.
Many current lithography apparatus have a large body structure that holds the projection lens, the metrology system and that supports the reticle stage and components of the illumination unit. FIGS. 1 and 2 show such an apparatus. In particular, body 20, which can be mounted on a base 100, includes one or more platforms and a plurality of columns, and supports a projection optical system 60 and a reticle stage 80. The metrology system also is mounted to the body 20. The metrology system includes laser interferometers 30 for measuring the position of the wafer stage 70, laser interferometers 40 for measuring the position of the reticle stage 80, and other sensors such as auto-focus sensors for measuring the vertical position of the wafer and/or reticle and alignment microscopes, etc. (generally represented by 50).
The body 20 is designed to hold all of the metrology elements in a fixed position relative to the projection optical system 60. Of course, some vibrations and distortions occur and cause degradation of the lithography apparatus performance.
One problem with existing lithography apparatus is that the body 20 is a relatively large structure, and therefore has undesirably low vibration frequencies. One contributing factor to the large size of the body is that the stage interferometers 30 and 40 are located relatively far from the projection optical system. Accordingly, when the interferometers are mounted to the same body that supports the projection optical system and other components of the lithography apparatus, that body becomes large.